Simplify the expression. $(5x^{3}+7x^{2}+4x)(7x)$
First use the distributive property. $ 5 x^3 (7 x) + 7 x^2 (7 x) + 4 x (7 x) $ Simplify. $35x^{4}+49x^{3}+28x^{2}$